Many portable electronic devices, such as laptop computers, personal digital assistants, cellular communications devices, and portable game or entertainment devices, can be powered by way of an internal battery as well as by way of an alternating current source through a suitable power adapter. The power adapter may convert 110 or 220 volts alternating current (VAC) to a lower voltage direct current (DC) signal that can be used by the electronic device. In some cases, the power adapter may accept a direct current input from an automobile or an aircraft power source in order to provide power to operate the electronic device.
When the electronic device is a portable computing device such as a laptop computer, for example, the laptop computer may require an amount of power that is beyond the capability of a particular power adapter. Thus, for example, a user may be operating a laptop computer that consumes 75 watts, while an associated power adapter is only capable of sourcing 55 watts of power. This scenario can be brought about by the user operating the laptop computer using a power adapter that may not have been specifically intended for use with the particular model of laptop computer which the user is attempting to operate. In another instance, the user may be attempting to operate the laptop computer on an airplane, in which the airplane power adapter is a general-purpose direct current source that is limited in the amount of power that can be output from the adapter. In either case, it is generally undesirable to operate the laptop computer using a power adapter that is not capable of providing adequate power.
In the event that the user attempts to operate an electronic device using a power adapter that is not capable of providing adequate power, the electronic device may operate unpredictably or not at all. Further, the power adapter may be permanently damaged or operate at an unacceptably high temperature. In some cases, such as when using a DC power adapter on an airplane, the DC power adapter may include circuitry that interrupts the operation of the supply in the event that the supply current exceeds a rated value. In this case, the user would be required to operate the device without the assistance of DC current supplied by the aircraft.